Rubber-modified thermosets and process i

ABSTRACT

IMPROVEMENTS I IMPACT STRENGTH AND FATIGUE PROPERTIES IN THERMOSET MATERIALS ARE MADE BY INCORPORATING THEREIN PARTICULATE GRADED-RUBBER HAVING SURFACE FUNCTIONILITY FOR REACTION WITH CONSTITUENTS OF THE THERMOSETS. A VARIETY OF NOVEL THERMOSET MATERIALS ARE PRODUCED UNDER VARIATONS OF THIS PROCESS. THE GRADED-RUBBER PARTICLES ARE CHARACTERIZED BY HAVING A RUBBERY CORE AND A GLASS-LIKE POLYMERIC OUTER SHELL.

United States Patent M US. Cl. 260-836 20 Claims ABSTRACT OF THEDISCLOSURE Improvements in impact strength and fatigue properties inthermoset materials are made by incorporating therein particulategraded-rubber having surface functionality for reaction withconstituents of the thermosets. A variety of novel thermoset materialsare produced under variations of this process. The graded-rubberparticles are characterized by having a rubbery core and a glass-likepolymeric outer shell.

This application is a divisional application of US. Patent ApplicationSer. No. 100,465, filed Dec. 21, 1970, now abandoned.

THE INVENTION This invention is concerned with the modification ofthermoset materials to provide improvements in their impact strength andfatigue properties. This invention has application to the broad spectrumof thermoset materials and involves the chemical incorporation ofparticulate materials having unique rubber-like properties with theconstituents of a thermoset reaction system. Thermosets of thisinvention are compatible with conventional molding techniques, e.g.,compression, injection, etc., and applicable to the production ofstructural material as, for instance, automobile body panels, electricalappliance housings, boat construction, storage tanks, conduits,particularly those for the transmission of heated fluids, etc. Thesethermosets also have application in the coatings field as, for instance,in radiation curable paints.

In most instances, the thermoset constituents, exclusive of theparticulate material hereinafter described, will include a reactiveprepolymer and where applicable a crosslinking agent. The particulatematerial is provided with surface functionality that will react witheither the prepolymer or the crosslinking agent or both.

The prepolymer may be a conventional thermoset constituent of awell-known thermoset system, e.g., a phenolformaldehyde resin, amelamine-formaldehyde resin, an alpha-beta olefinically unsaturatedresin, resins of any of the epoxy-carboxy, epoxy-epoxy, epoxy-aminecrosslinking systems, and others.

The unique particulate material which may be termed graded rubber has arubber-like, elastomeric core of crosslinked acrylic polymer, aglass-like outer shell consisting essentially of a copolymer of about 30to about 99 molar parts of methyl methacrylate and about 1 to about 70molar parts of monomers copolymerizable with methyl methacrylate, atleast one of which provides the particle with the desired surfacefunctionality, and an intermediate layer consisting essentially of thecopolymerization produgtnof monomers used to form the core and the outers e Particulate material of the same description excepting that thesurfaces are non-functional, e.g., polymethylmethacrylate, may be usedto modify these thermosets but the desirable properties obtainable withthe preferred embodiments are materially diminished.

3,833,683 Patented Sept. 3, 1974 The concentration of graded-rubberparticles hom0- geneously dispersed in the final product can be variedover a wide range in conformance with the properties desired for suchproduct. Thus, it may be advisable in certain instances for thisconcentration to range upward from a minimum modifying amount to a majorfraction by weight. In the main, however, the concentration andcomposition of the graded-rubber particles will be such that theclastomeric cores will comprise a minor proportion by weight of thefinal product, commonly between about 5 and about 40, more commonlybetween about 10 and about 30, weight percent of the final product. Theweight relationship of the glass-like outer shell to the elastomericcore can be varied but for most purposes the weight. of the outer shellwill not substantially exceed that of the core. In most instances, theaverage weights of the outer shells will be about 10 to 60, preferablyabout 20 to about 50 percent of the average weight of the cores.

Preparation of the Graded-Rubber Particles The process for preparingthese particulate materials is at least a two-stage process. A majoramount of monofunctional monoacrylate is emulsion copolymerized in thefirst stage with a crosslinking amount of a dior tri-functional monomercontaining two or more non-conjugated terminal ethylenic groups,preferably a diacrylate, using a watersoluble free radical initiator anda suitable surfactant to yield a latex of relatively uniform particlesize, e.g., 0.04 to 1 micron average diameter. Before this reactionreaches substantial completion, i.e., when the reaction is between about50 and about 90, preferably between about 70 and about 89, percentcomplete, the second stage monomeric component, i.e., methylmethacrylate and one or more monomers copolymerizable therewith, isadded slow- 1y to the reaction mixture. The polymerization process iscontinued to yield a stable latex of relatively uniform particle sizeand composition as evidenced by electron microscopy. Additionalsurfactant may be added simul- 'taneously with the second stagemonomeric component.

The latex is coagulated, washed, and dried to yield a finely dividedwhite powder which is suitable for blending with other constituents.

Generally, the particles are prepared from monomers that will provide acrosslinked, acrylic, rubber-like core and a glass-like polymeric outershell at room temperature, e.g., 20-30 C. The terms rubber-like andglass-like are, of course, meaningless except when used in reference toa specific temperature or temperature range. The particles should beformulated so that when molded the core retains such rubber-likeproperties and the outer shell retains its glass-like properties at alltemperatures encountered by articles of. commerce in the intended fieldof use. Hence, for practical purposes, the monomer should be selected sothat the core has a glass transition temperature that is substantiallybelow that of the outer shell. Advantageously, the difference in glasstransition temperatures between the core and shell is at last 50 0,preferably above C.

The core is formed from a major amount of an alkyl acrylate and acrosslinking amount of a dior tri-functional monomer containing two ormore non-conjugated terminal ethylenic groups. The monofunctional alkylmonoacrylate is preferably an ester of a C -C monohydric alcohol andacrylic acid, e.g., ethyl acrylate, butyl acrylate, hexyl acrylate,2-ethyl hexyl acrylate and/or mixtures of the same. Certain other alkylacrylates may be used when the crosslinked polymer thereof has anappropriate glass transition temperature, e.g., dodecyl methacrylate.Butyl acrylate and 2-ethyl hexyl acrylate are the most preferred of themonoacrylates for use in forming the core. The polymers produced frommost methacrylates have glass transition temperatures which are too highto provide rubber-like properties at normally encountered temperatures.Hence, except for special applications, the monoacrylate component ofthe core will be either an ester (or esters) of acrylic acid or amixture of a major amount of the same and a minor amount ofmethacrylates.

Suitable crosslinking agents include, but not by way of limitation,1,3-butylene diacrylate, 1,3-butylene dimethacrylate, divinyl benzene,1,6-hexamethylene diacrylate, 1, G-hexarnethylene dimethacrylate,1,1,1-trimethylol ethane triacrylate, 1,1,l-trimethylol ethanetrirnethacrylate, 1,1,1- trimethylol propane triacrylate,l,l,l-trirnethylol propane trimethacrylate 1,4- cyclohexane dimethanoldimethacrylate, allyl acrylate, allyl methacrylate, methallyl acrylate,methallyl methacrylate, diallyl maleate, diallyl furnarate, and diallylphthalate. In one embodiment, the crosslinking agent is a diester ofacrylic or methacrylic acid and a C -C preferably C -C dihydric alcohol.

In the first stage reaction, there is preferably employed about 80 toabout 98 mole percent of the monofunctional monoacrylate and about 20 toabout 2 mole percent of the crosslinking agent. In the second stagereaction, the mixture of methyl methacrylate and monomerscopolymerizable therewith are added before the first reaction J ceases.The amounts of the second stage reactant or reactants relative to thecombined first stage reactants may vary widely depending upon thephysical properties desired in the moldings produced from theseparticles, i.e., from about 10 to about 90 to about 90 to about 10weight percent.

The particulate materials can be prepared with a variety of differentfunctional groups on the surfaces for reaction With thermosetconstituents. This functionality includes, but is not limited to epoxy,carboxy, and hydroxy functionality. The outer shell is formed frommethyl methacrylate and a balance of monomers copolymerizable therewith,at least one of which is difunctional. The minimum concentration ofmethyl methacrylate in the mono- 'rner mix will 'be about mole percent.In one such embodiment, the monomer mix used will contain about 30 toabout 99 mole percent methyl methacrylate, t) to mole percent of acompound or compounds selected from monovinyl hydrocarbons and othermonofunctional acryl- I ates, and about 1 to about 45, advantageouslyabout 5 to about 40, and preferably about 10 to about 35 mole percent ofone or more difunctional monoacrylates such as glycidyl methacrylate,hydroxyethyl methacrylate, by-

droxy-ethyl' acrylate, hydroxypropyl acrylate, hydroxypropy]methacrylate, mixtures thereof, and/or other employed are preferably themonofunctional monoacry lates and/or monofunctional vinyl hydrocarbons.Suitable monofunctional monoacrylates for this purpose include esters ofacrylic or methacrylic acid with a monohydric alcohol, preferably a C toC monohydric alcohol, e.g., ethyl acrylate, butyl acrylate, butylmethacrylate, and 2- ethyl hexyl acrylate. A minor amount of higheralkyl acrylate, e.g., .dodecyl methacrylate, may also be used. Suitablemonovinyl hydrocarbons for this purpose include styrene, alpha-methylstyrene, and vinyl toluene. Depending upon the end product desired, itwill sometimes be advantageous to have a limited amount of crosslinkingin the outer shell and hence to include with the methyl methacrylate andthe difunctional monoacrylate a minor amount of a diacrylate or divinylhydrocarbon, e.g., divinyl benzene or 1,3-butylene diacrylate.

, The physical properties of the outer shell may be otherwise modifiedby replacing up to about 30 mole percent of the monctunctionalmonoacrylate with acrylonitrile or methacrylonitrile. Likewise, one mayreplace up to about 30 mole percent of the monofunctional monoacrylatesheretofore mentioned with an cquimolar amount of isobornyl methacrylate.In each of these embodiments, as in all others, the monomer mix used toform the outer shell will contain at least about 30 mole percent methylmethacrylate.

It is also within the scope of this invention to carry out furtherreactions after particle formation, as for instance, to react a diortrifunctional monomer with a functionality of said surface in order toalter the character or functionality of said surface, e.g., acrylic ormethacrylic acid with epoxy-functional particles. In other embodiments,a carboxy or hydroxy functional particle may be reacted with an acylhalide e.g., methacrylyl chloride, and the resultant product furtherreacted in the thermoset system.

The initial monomer charge is usually emulsified by one or moremicelle-forming compounds composed of a hydrophobic part, such as ahydrocarbon group containing eight or more carbon atoms, and ahydrophilic part, such as alkali metal or ammonium carboxylate groups,phosphateor sulfate partial ester groups, sulfonate groups, and thelike. Exemplary emulsifying agents include alkali metal sulfonates ofstyrene, naphthalene, decyl benzene, and dodecyl benzene; sodium dodecylsulfate; sodium stearate; sodium oleate; the sodium alkyl arylpolyoxymethylene sulfates and phosphates; the ethylene oxide condensatesof long chain fatty acids, alcohols, and mercaptans, and the alkalimetal salts of rosin acids. These materials and the techniques of theiremployment in emulsion formation and maintenance are well known to theart. As they are conventional materials employed in a conventionalmanner, further description and explanation are unnecessary.

The polymerization initiator is composed of one or more water-soluble,free-radical-generating species such as hydrogen peroxide or the sodium,potassium, or ammonium persulfates, perborates, peracetates,percarbonates, and the like. As is well known in the art, theseinitiators may be associated with activating systems such as redoxsystems which may incorporate mild reducing agents such as sulfites andthiosulfites and redox reaction promoters such as transition metal ions.

A chain transfer agent or a mixture of chain transfer agents may beadded to the reaction medium to limit the molecular weight of thepolymer; such chain transfer agents are generally mercaptans such asdodecanethiol; benzenethiol, pentanethiol, and butanethiol.

Those skilled in the art will be aware that other emulsifying agents,polymerization initiators and chain transfer agents may be used whencompatible with the polymerization system herein employed.

The reaction may be carried out at temperatures from about 40 C. to C.,or at lower temperatures, as from 0 C. to 80 C. in the case of activatedsystems. i

Determination of the concentration of reactive epoxy groups on the shellof the graded-rubber particles can be made by the method involvingaddition of tetraethylammonium bromide followed by titration withperchloric acid in acetic acid using crystal violet as indicator. Thismethod is described by R. R. Jay in Analytical Chemistry, Vol. 36, page667 (1964). Determination of the concentration of reactive hydroxylgroups on the shell of the graded-rubber particles can be made by thewell-known method of analysis wherein the hydroxy groups are reactedwith acetic anhydride using a pyridine catalyst. The acetic acidproduced is then back titrated with sodium hydroxide. For details, seeSteyermark, Quantitive Organic Analysis, pages 302-303, published byBlakiston Company, New York, Toronto, and Philadelphia (1951). Fordetermination of hydroxyl groups, carboxyl groups and molecular weightalso see the methods described by W. R. Sorenson and T. W. Campbell inPreparative l /I e t i 1;x

ods of Polymer Chemistry, Interscience Publishers, New York, NY, USA.(1961) at page 134.

This invention will be more fully understood from the following exampleswhich illustrate the modification of typical thermoset materials withthe hereinbefore described graded-rubber particles.

Example 1 A polyester prepolymer, known hereinafter as Resin A, isprepared according to procedures well known in the art from an equimolarmixture of orthophthalic acid and maleic anhydride and neopentyl glycolin an amount 5% in excess of the stoichiometric requirement.

To 1000 parts by weight water which has been boiled and cooled to roomtemperature under a nitrogen atmosphere are added 2.86 parts by weightsodium dodecyl sulfate dissolved in 35.7 parts by weight water and aboutA; of a monomer mixture consisting of 348 parts by weight butyl acrylateand 32.3 parts by weight 1,3-butylene dimethylacrylate. The mixture isstirred to establish dispersion of the monomers. To the stirred mixtureare added 3.14 parts by weight potassium persulfate dissolved in 71.4parts by weight water. The mixture is heated to 45 C. After aboutminutes, addition of the remainder of the first monomer mixture is begunat a rate such that the temperature of the reaction mixture ismaintained at 47 to 49 C. The last half of the first monomer mixture isadded simultaneously with 2.86 parts by weight of sodium dodecyl sulfatedissolved in 35.7 parts by weight water. Addition of the first monomermixture requires about 45 minutes. The reaction mixture is maintained at47 to 49 C. for 35 minutes prior to beginning simultaneous dropwiseaddition of (1) a mixture of 236 parts by weight methyl methacrylate,143.4 parts by weight glycidyl methacrylate, and 2.57 parts by Weightl-dodecanethiol, and (2) a solution of 5.72 parts by weight sodiumdodecyl sulfate in 35.7 parts by weight water. This addition, whichrequires about 40 minutes, is carried out at such a rate that thetemperature of the reaction mixture is maintained at 47 to 49 C.Following this addition, the mixture is maintained at 47 to 49 C. for anadditional two hours. The resulting latex, known hereinafter as Latex A,is cooled to room temperature and neutralized with aqueous ammonia. Theoverall conversion of monomers is about 98%. The average size of theseparticles is in the range of 0.1 to 0.2 micron.

Latex A is coagulated by adding one volume of latex to approximately 4volumes of methyl alcohol to which has been added 0.001 volumeconcentrated hydrochloric acid. The coagulum is isolated by filtration,washed with several volumes of methyl alcohol, and with water, and isdried in vacuo to yield Powder A.

Twenty parts by weight of Powder A are dispersed in 200 parts by weightunpurified commercial styrene monomer. To this dispersion is addedmethacrylic acid in an amount providing about one carboxyl group pereach epoxy group in the outer shells of the rubber particles and acatalytic amount (0.1 parts by weight based on methacrylic acid) benzyltriethyl ammonium chloride. The dispersion is heated until the reactionbetween the methacrylic acid and the epoxy groups on thegradedelastomeric particles is at least 50% complete.

The resulting dispersion is blended with an appropriate amount (ashereinafter defined) of Resin A and benzoyl peroxide. Sufiicient styrenemonomer is removed by vacuum distillation to yield a final moldingcomposition comprising 20% by weight rubber (based on the core portionof the graded-rubber particles) for a total of 40% by weightgraded-rubber particles and 60% by weight polyester-styrene present inweight ratio 65:35; the benzoyl peroxide concentration is 2% by weightbased on polyester-styrene content. The blend is molded for minutes at115 C. and postcured at 120 C. for three hours to yield a hard,acetone-insoluble article. Room temperature tensile properties are givenbelow:

Elongation-to-break, percent 7.5 Stress at break, p.s.i 5,700 Modulus,p.s.i 292,000

Example 2 For purposes of comparison, Resin A is blended with styrenemonomer in weight ratio 65:35 and 2% by weight benzoyl peroxide isadded. The blend is molded at C. for 15 minutes and postcured at C. forthree hours to yield a hard, acetone insoluble article. Room temperaturetensile properties are given below:

Elongation-to-break, percent 3.1 Stress at break, p.s.i 8,100 Modulus,p.s.i 418,000

Example 3 The procedures of Example 1 are repeated with the differencethat acrylic acid replaces methacrylic acid in the modification of thegraded-rubber particles.

'Example 4 To 1000 parts by Weight water which has been boiled andcooled to room temperature under a nitrogen atmosphere are added 2.86parts by weight sodium dodecyl sulfate dissolved in 35.7 parts by weightwater and about of a monomer mixture consisting of 521 parts butylacrylate and 48.5 parts by weight of 1,3-butylene dimethacrylate. Thismixture is stirred to establish dispersion of the monomers and 3.14parts by weight potassium persulfate dissolved in 71.4 parts by weightwater are added to the stirred mixture. This mixture is heated to 45 C.After about 10 minutes, addition of the remainder of the first monomermixture is begun at a rate such that the tem perature of the reactionmixture is maintained at 47 to 50 C. During the addition of the lasttwo-thirds of the first monomer mixture, 5.72 parts by weight sodiumdodecyl sulfate dissolved in 35.7 parts by weight water are added at asubstantially constant rate. The reaction mixture is maintained at 47 to50 for about 40 minutes prior to beginning simultaneous dropwiseaddition of 1) parts by weight of a monomer mixture consisting of methylmethacrylate, styrene, and glycidyl methacrylate present in mole rate35:35:30, and (2) 2.86 parts by weight sodium dodecyl sulphate dissolvedin 35 .7 parts by weight water. This addition is carried out at such arate that the mixture is maintained at 47 to 50 C. Following thisaddition, the temperature is held at 47 to 50 C. for an additional twohours. The resulting latex known as Latex B, is cooled to roomtemperature.

A portion of Latex B is coagulated by adding one volume of latex rapidlybut dropwise to approximately four volumes of rapidly stirred methylalcohol which has been heated to about 60 C. before beginning thecoagulation. The resulting coagulum is filtered, washed, and dried invacuo to yield a white powder hereinafter known as Powder B.

Twenty parts by weight of Powder B are dispersed in 200 parts by weightunpurified commercial styrene monomer. To this dispersion is addedmethacrylic acid in an amount providing about one carboxyl group pereach epoxy group in the outer shells of the rubber particles and acatalytic amount (0.1 parts by weight based on methacrylic acid) benzyltriethyl ammonium chloride. The dispersion is heated until the reactionbetween the methacrylic acid and the epoxy groups on thegradedelastomeric particles is at least 50% complete.

The resulting dispersion is blended with an appropriate amount of ResinA (alpha-beta olefinically unsaturated polyester) and benzoyl; styrenemonomer is removed by vacuum distillation to yield a molding materialcomprising 20% by weight rubber (based on the core portion of thegraded-rubber particles) for a total of 26.7% by weightElongation-to-break, percent 6.2 Stress at break, p.s.i 7,200 Modulus,p.s.i 300,000

Example The procedures of Example 4 are repeated with the differencethat acrylic acid replaces methacrylic acid in the modification of thegraded-rubber particles.

Example 6 The composite molding material of Example 4 is used inpreparation of a glass fibre reinforced composite containing 20% byvolume 1%" polyester compatible chopped glass fibres. Room temperaturetensile properties of this material as well as of a composite based onthe polyesterstyrene molding compound of Example 2 containing 20% byvolume Vs" chopped glass fibres are given below:

Elongation Stress to break, at break, Modulus, percent p.s.i. p.s.i.

PolyesterlstyreneIglass mold 0. 7 8, 300 1, 400, 000Polyester/styrene/rubber glass mold 1. 2 12, 000 1, 100, 000

In addition to displaying markedly superior strength, therubber-reinforced glass-containing composite displays much betterretention of modulus on repeated stressing.

Example 7 The procedures of the preceding examples are repeated with thediiference that the polyester resin is formed from an equimolar mixtureof orthophthalic acid and maleic anhydride with propylene glycol in anamount 5% in excess of the stoichiometric requirement.

Example 8 The procedures of the preceding examples are repeated with thedifference that vinyl toluene is substituted for styrene.

Example 9 A thermoset prepolymer emulsion is prepared in the followingway: To 800 parts by weight water which has been boiled and cooled toroom temperature under a nitrogen atmosphere are added 4 parts by weightsodium dodecyl sulfate in 25 parts by weight water and about one-thirdof a mixture consisting of 186.6 parts by weight methyl methacrylate,113.4 parts by weight glycidyl methacrylate, and 2.0 parts by weightl-dodecanethiol. The mixture is stirred to establish dispersion of themonomers. To the stirred mixture is added 3.2 parts by weight potassiumpersulfate dissolved in 75 parts by weight water. The mixture is heatedto about 55 C. After the initial exotherm has subsided, the remainder ofthe monomer mixture is added at a rate such that the temperature of thereaction mixture is maintained at about 55 C. Following this addition,the reaction mixture is maintained at about 55 C. for an additional twohours. The resulting latex is cooled to room temperature and blendedwith a sutficient amount of Latex A (Example 1 epoxy-functional rubberparticles) to yield a molding compound containing about 25% rubber(based on the core portion of the graded-rubber particles). The mixedemulsion is coagulated by adding one volume of latex to approximately8-10 volumes of methyl alcohol acidified with 0.001 volume concentratedhydrochloric acid. The coagulum is further washed with methyl alcohol, acatalytic amount (about 1% by weight based on the epoxy-bearing portionof the blend) of 2-ethyl-4-methyl-imidazole is added, and a moldingpowder is isolated by drying in vacuo. The molding powder is compressionmolded at 400 F. for 15 minutes to yield a hard article which is bycomparison much tougher than a similar article prepared withoutincorporation of graded-rubber particles. Room temperature tensileproperties of both materials are given below:

Elongation Stress to break, at break Modulus, percent p.s.i. p.s.i.

Molded article without rubber 2. 2 8, 200 460, 000 Molded article withrubber 27. 0 6, 100 260, 000

Example 10 The procedures of Example 9 are repeated with the difierencethat Latex B (Example 4 epoxy-functional rubber particles) issubstituted for Latex A (Example 1) in the preparation of the blend.

Example 11 Elongation Stress to break, at break, Modulus, percent p.s.i.p.s.i

Molded article without rubber but with glass fibre 0.7 5, 900 1, 960,000 Molded article with rubber and glass fibre 1. 0 7, 400 1, 160, 000

The rubber modified material shows markedly im proved strength.Furthermore, the rubber modified material displays much better retentionof modulus on repeating stressing.

Example 12 A thermoset prepolymer is prepared by adding a mixture of30.0 parts by weight methacrylic acid, 23.4 parts by weightmethacrylonitrile, 46.6 parts by weight methyl methacrylate, and 3.7parts by weight di-t-butyl perbenzoate slowly, dropwise over a three tofour hour period to sufficient refluxing dioxane to result in a finalconcentration of polymer of about 30% by weight. The solution iscoagulated by dropwise addition to 5 to 7 volumes of rapidly stirredhexane. The prepolymer is filtered and dried in vacuo. A 20% by weighttotal solids solution is then prepared in dioxane comprising theprepolymer, a stoichiometric amount of the diglycidyl ether of BisphenolA, and a catalytic amount (about 1.0% by weight based on prepolymer) ofN, N-dimethyl benzyl amine. This solution is used in preparation ofrubber reinforced molding compounds in the following way. A latex isprepared according to the procedures given for Latex A (Example 1) withthe differences that 1) the first monomer mixture comprises mole percentbutyl acrylate and 10 mole percent 1,3-butylene dimethacrylate and (2)the second monomer mixture comprises 45 mole percent methylmethacrylate, 45 mole percent glycidyl methacrylate, and 10 mole percent1,3-butylene dimeth acrylate. This latex is coagulated by addition ofone volume of latex to four volumes of methanol acidified with 0.001volume concentrated hydrochloric acid. The coagulum is isolated bygentle centrifugation and is subsequently dispersed (without drying) indioxane to yield a dispersion containing about 15% solids. Thisdispersion is blended with the thermoset prepolymer-crosslinker catalystsolution; the mixture is freeze-dried and the resulting molding powderis compression molded to yield a hard article insoluble in acetone.Elongation-to-break is found to be monotonically increasing function ofrubber content, at least up to 25% by weight rubber (based on the coreportion of the graded-rubber particles). Specimens containing 25% weightrubber (based on the core portion of the graded-rubber particles) arefound to have an elongation-to-break at least double that of specimensomitting the rubber.

Example 13 The procedures of Example 12 are repeated with the differencethat the shell of graded-rubber particles is formed from a monomermixture comprising essentially 95 mole percent methyl methacrylate andmole percent methacrylic acid.

Example 14 An acrylic thermoset prepolymer of a different type isprepared by slowly adding a mixture of 600 parts by weight glycidylmethacrylate, 140.0 parts by weight methyl methacrylate, and 4.0 partsby weight 2,2 azobis [Z-methylpropionitrile], to 200 parts by weightrapidly stirred toluene maintained at reflux temperature under anitrogen atmosphere. Upon completion of the addition, 0.2 parts byweight 2,2-azobis [Z-methylpropionitrile] dissolved in 25 parts byweight toluene is added over a thirty minute period. The reactionmixture is maintained at 110 C. for an additional two hours. Thereaction mixture is then cooled to below 50 C. and there is added 34parts by weight methacrylic acid, 1.5 parts by weight benzyl triethylammonium chloride, and 0.2 parts by weight hydroquinone. The mixture isstirred at 85 C. for several hours until titration shows more than 95%of the methacrylic acid reacted and infrared analysis shows more than 95of the glycidyl group consumed. The reaction mixture is cooled, dilutedwith toluene to 30% solids, and coagulated in 5 to 7 volumes of hexane.The resultant white powder hereinafter referred to as Powder C is driedin vacuo for four hours at 60 C.

About 70 parts by weight Powder A (Example 1 epoxyfunctional rubberparticles) are dissolved in 150 parts by weight acetone. To thissolution is added methacrylic acid in an amount providing about onecarboxyl group per each epoxy group in the outer shells of the rubberparticles. To the mixture is added a catalytic amount (1.5 parts byweight) benzyl triethyl ammonium chloride. The dispersion is heateduntil reaction between the methacrylic acid and the epoxy groups on thegraded-rubber particles is substantially complete. The rubber particlesare separated from the acetone, dried, and dispersed in 150 parts byweight methyl methacrylate. To this dispersion are added 200 parts byweight Powder C (unsaturated acrylic prepolymer and a catalytic amount(0.1 percent by weight) di-t-butyl peroxide. The dispersion iscompression molded at 100 C. for 15 minutes to yield a hard articleinsoluble in acetone. By comparison, this mold is much tougher than anidentically prepared mold which omits the graded-elastomeric particles.

Example 15 The procedures of Example 14 are repeated with the differencethat Powder C (unsaturated acrylic prepolymer) is replaced by aprepolymer prepared in the following way: A mixture of 70 parts byweight glycidyl methacrylate, 90 parts by weight methyl methacrylate, 40parts by weight methacrylonitrile, and 4 parts by weight 2,2-azobis-[2-methylproprionitrile] is added slowly to a refluxing mixtureof 150 parts by weight toluene and 150 parts by weight dioxane under anitrogen atmosphere. The prepolymer obtained is reacted with 45 parts byweight methacrylic acid using 1.5 parts by weight benzyl triethylammonium chloride as catalyst in the presence of 0.2 parts by weighthydroquinone. Upon completion of this reaction, the mixture is dilutedwith acetone to 30% by weight solids and is coagulated in 5 to 7 volumesof hexane. The resultant white powder hereinafter referred to as PowderD is dried in vacuo at 60 C. for four hours.

Upon substitution of Powder D for Powder C in Example 14, a hard moldedarticle is obtained which is insoluble in acetone or toluene. Bycomparison, the molded piece is much tougher than an identicallyprepared molded piece which omits the graded-rubber particles.

Example 16 The procedures of Examples 14 and 15 are repeated with thedifference that an equimolar amount of acrylic acid is substituted formethacrylic acid in the reaction with the epoxy groups on the surfacesof the graded-rubber particles.

Example 17 Another thermoset is prepared with incorporation of thegraded-rubber particles in the following manner: Sixty parts by weightglycidyl methacrylate, 140 parts by weight methyl methacrylate, 4 partsby weight 2,2'-azobis-[2- methylpropionitrile], and 6 parts by weightl-dodecanethiol are mixed and added to 600 parts by weight water(freshly boiled to remove dissolved oxygen and cooled to roomtemperature under a nitrogen atmosphere) which contains 1.8 parts byweight polyvinyl alcohol and 18 parts by weight sodium chloride.

The mixture is stirred vigorously and gently heated to 50 C. When anexothermic reaction is observed, external heating is discontinued. Thereaction mixture is maintained at 60 C. for three hours. The polymerthus obtained is filtered, washed with methyl alcohol, and dried invacuo at 60 C. for six hours.

One hundred-ninety parts by weight of the powder obtained is mixed with150 parts by weight methyl methacrylate, 140 parts by weight Powder A(Example 1 functional rubber particles), suflicient methacrylic acid toprovide about one acid functionality per each epoxy group in themixture, one part by weight benzyl triethyl ammonium chloride, and 0.2parts by weight hydroquinone. Dispersion of the rubber particles isachieved by blending with a Brabender mixer equipped with sigma blades.The mixture is heated to C. until the reaction between acid groups andglycidyl groups is substantially complete. One weight percent di-t-butylperbenzoate is added and the mixture is compression molded for 15minutes at C. to yield a hard molded article which is insoluble inacetone.

Example 18 The procedures of Example 17 are repeated with the differencethat the thermoset prepolymer is formed from a monomer mixturecomprising 30 mole percent glycidyl methacrylate, 30 mole percentmethacrylonitrile, and 40 mole percent methyl methacrylate.

Example 19 The procedures of Examples 14-18 are repeated with thedilference that the dispersion of prepolymer, methyl methacrylate, andgraded-rubber particles is diluted with methyl methacrylate until thetotal concentration of unreacted methyl methacrylate is 40 weightpercent. This material is sprayed on wood, metal, and polymericsubstrates and cross-linked thereon by exposing the resultant coating toan electron beam having average energy of about 295,000 electron voltsin a nitrogen atmosphere.

Example 20 Graded-rubber particles are prepared according to theprocedure given in Example 4 for Powder B (epoxy-functional rubberparticles) with the difference that the outer shell of the particles isformed from a monomer mixer comprising methyl methacrylate, butylacrylate, and glycidyl methacrylate present in mole ratio 35:35:30; thismaterial is crushed to a very fine powder at about 80 C. and ishereinafter referred to as Powder E. The latex precursor of Powder E isdesignated Latex E.

One hundred parts by weight of a commercial grade DGEBA (diglycidylether of Bisphenol A) of equivalent weight about 190 is mixed with tenparts by weight phenyl glycidyl ether, twelve parts by weighttriethylene tetramine, and fifty parts by weight Powder E. The mixtureis thoroughly blended using a Brabender mixer equipped with sigmablades. The mixture is molded and allowed to cure at room temperaturefor seven days followed by-a two hour postcure at 60 C. to yield a hard,translucent, rubber-modified epoxy resin.

Example 21 Two hundred parts by weight Latex E (epoxy-functional rubberparticles) are blended with 100 parts by weight wood flour. The mass isdried in vacuo at 40 C. for 24 hours, blended with 100 parts by weightof a commercial grade DGEBA of equivalent weight 190 and three parts byweight boron trifluoride monoethylamine. The mixture is molded at 120 C.for one hour followed by a postcure at 150" C. for two hours.

Example 22 Twenty parts by weight Powder E (Example 20 epoxyfunctionalrubber particles) are dispersed in 200 parts by weight benzene. To thisdispersion is added acrylic acid in an amount providing about onecarboxyl group per each epoxy group in the outer shells of the rubberparticles, 0.2 parts by weight hydroquinone and a catalytic amount (0.1parts by weight based on acrylic acid) of benzyl triethyl ammoniumchloride. The dispersion is heated until reaction between the acrylicacid and the glycidyl groups on the rubber particles is substantiallycomplete.

To the resulting dispersion is added a benzene solution of sixty partsby weight of an allyl prepolymer (formed by partial polymerization ofdiallyl phthalate according to procedures well known in the art). Themixture is freezedried and crushed to a powder. Two percent by weightd-t-butyl perbenzoate is added and the molding powder is compressionmolded at 175 C. for 15 minutes to yield a hard, translucent,rubber-modified allyl resin.

Example 23 and compression molded at 150 C. for 15 minutes to yield ahard article insoluble in acetone.

Example 24 Fifty parts by Weight finely ground novolac(phenolformaldehyde resin), 50 parts by weight dry wood flour, 7 partsby weight hexamethylene-tetramine, 2 parts by weight magnesium oxide, 1part by weight calcium stearate, and 20 parts by weight Powder E(unsaturated epoxy-functional rubber particles) are blended in a ballmill. The blend is compression molded at 160 C. for 5 minutes to give ahard, insoluble article.

Example 25 Graded-rubber particles are prepared in accordance with theprocedure of Latex B of Example 4 with the difference that the particlesare provided with hydroxy functionality by substituting an equimolaramount of hydroxyethyl methacrylate for the glycidyl methacrylate. Thehydroxy-functional graded-rubber particles are incorporated into athermoset molding system employing the following procedure: Thegraded-rubber particles are isolated as a powder and blended in a ballmill with a sufiicient amount of solid epoxy resin (e.g., a condensateof epichlorohydrin and Bisphenol A of molecular weight about 1,000) toobtain a final rubber concentration (based on the core portion of therubber particles) of 20% by weight. One hundred parts by weight of theresulting powder is heated to C., and 20 parts by weight molten phthalicanhydride is added. The mixture is molded at 120 C. for one hour,followed by two hours at C. to yield a hard insoluble article.

Example 26 The procedure of Example 25 is repeated except for thedifference that an equimolar amount of hydroxyethyl acrylate issubstituted for the hydroxyethyl methacrylate.

Example 27 The procedure of Example 25 is repeated except for thedifference that an equimolar amount of hydroxypropyl methacrylate issubstituted for the hydroxyethyl methacrylate.

Example 28 The procedure of Example 25 is repeated except for thedifference that an equimolar amount of hydroxypropyl acrylate issubstituted for the hydroxyethyl methacrylate.

Example 29 The procedure of Example 1 is repeated except for thedifference that in the preparation of the polyester prepolymer there issubstituted an equimolar amount of tetrahydrophthalic anhydride for theorthophthalic acid and an equimolar amount of fumaric acid for themaleic anhydride.

Example 30 The procedure of Example 1 is repeated except for thedifference that in the preparation of the polyester prepolymer, anequimolar amount of cyclohexane dicarboxylic acid is substituted for theorthophthalic acid and an equimolar amount of propylene glycol issubstituted for the neopentyl glycol.

Example 31 The procedure of Example 1 is repeated except for thedifference that in the preparation of the polyester prepolymer there issubstituted an equimolar amount of ethylene glycol for the neopentylglycol and an equimolar amount of itaconic anhydride is substituted forthe maleic anhydride.

Example 32 The procedure of Example 1 is repeated except for thedifierence that in the preparation of the polyester prepolymer there issubstituted an equimolar amount of Z-butene- 1,4 diol for the neopentylglycol.

Example 33 The procedure of Example 1 is repeated except for thediiference in the preparation of the polyester prepolymer where there issubstituted an equimolar amount of 1,6- hexamethylene glycol for theneopentyl glycol.

EXAMPLE 34 The procedure of Example 1 is repeated except for thedifference in the preparation of the polyester prepolymer. An equimolaramount of 1,2-propanediol is substituted for the neopentyl glycol.

Example 35 13 added dropwise to the reaction mixture. The glycidylmethacrylate is mixed with the third portion and this mixture is thenadded dropwise to the reaction mixture.

Example 3 6 The procedure of Example 1 is repeated except for thedifference in the preparation of the graded-rubber particles wherein thecore is prepared from about 90 mole percent 2-ethyl hexyl acrylate and10 mole percent 1,3- butylene diacrylate and the monomer mixtureemployed to form the outer shell is a mixture of 40 molepercent methylmethacrylate, 10 mole percent acrylonitrile, 10 mole percent butylacrylate, 10 mole percent alpha methyl styrene and 30 mole percent ofglycidyl methacrylate.

Example 37 The procedure of Example 36 is repeated except for thedifference that glycidyl acrylate is substituted for the glycidylmethacrylate.

Example 38 The procedure of Example 1 is repeated except for thedifference in the preparation of the graded-rubber particles wherein thecore is prepared from about 90 mole percent butyl acrylate and about 10mole percent of divinyl benzene and the monomer mixture employed to formthe outer shell is a mixture of 60 mole percent methyl methacrylate, 30mole percent glycidyl methacrylate and 10 mole percent divinyl benzene.

The terms acrylate and acrylates, when used herein without a modifierdistinguishing between esters of acrylic and methacrylic acid, shall beunderstood to include both. This, of course, does not apply to thenaming of a specific compound.

The foregoing examples are illustrative of the invention defined in theamended claims. Those skilled in the art will be aware thatmodifications may be made therein without departing from the scope ofthe invention as set forth in the appended claims.

We claim:

1. In a method for forming a molded, thermoset, polymeric materialwherein a polymer of polymerized unsaturated compounds and acrosslinking agent reactive therewith are intimately mixed, molded andreacted with each other, the improvement wherein:

A. said crosslinking agent is a graded-rubber particle consistingessentially of (1) about 10 to about 90 weight percent of a core ofcrosslinked acrylic polymer consisting essentially of (a) a major amountof a monofunctional monoacrylate, constituting at a minimum about 80mole percent and (b) a minor and crosslinking amount of a di-ortri-functional monomer containing two or more non-conjugated terminalethylenic groups, not exceeding about 20 mole percent of the corereactants and (a) about 90 to about 10 weight percent an outer shellformed by polymerization of a mixture of monomers consisting essentiallyof about 30 to about 98 mole percent methyl methacrylate, to about 68mole percent of unsaturated monomers selected from monofunctionalmono-acrylates, diacrylates, monovinyl hydrocarbons, and divinylhydrocarbons, and about 2 to about 35 mole percent of a monomer havingan olefinic group reactable with said methyl methacrylate and anepoxy-functional group which (21) remains unreacted in saidpolymerization and (b) provides said shell with surface functionalitythat is reactive with said polymer, of polymerized unsaturated compoundsand B. said polymer of polymerized unsaturated compounds hasfunctionality selected from carboxy functionality, epoxy functionalityand hydroxy functionality and being present in a crosslinking amount.

2. A method in accordance with Claim 1 wherein said core is formed fromabout to about 98 mole percent of an ester of acrylic acid and a C -Cmonohydric alcohol and about 2 to about 20 mole percent of divinylbenzene, a diester of acrylic or methacrylic acid and a C -C dihydricalcohol or a triester of acrylic or methacrylic acid and a C -Ctrihydric alcohol.

3. A method in accordance with Claim 1 wherein said functionality ofsaid polymer of polymerized unsaturated compounds is carboxyfunctionality.

4. A method in accordance with Claim 1 wherein said functionality ofsaid polymer of polymerized unsaturated compounds is epoxyfunctionality.

5. A method in accordance with Claim 1 wherein said functionality ofsaid polymer of polymerized unsaturated compounds is hydroxyfunctionality.

6. In a method for forming a molded, thermoset, polymeric materialwherein a polymer of polymerized unsaturated compounds havingfunctionality selected from carboxy functionality, epoxy functionalityand hydroxy functionality and a polyepoxide having at least two epoxygroups per molecule reactive therewith in crosslinking amounts areintimately mixed, molded and reacted with each other, the improvementwherein said polymer and said polyepoxide are intimately mixed prior tomolding with graded rubber particles having surface epoxy functionalitythat is reactive with said polymer, said polyepoxide or both saidpolymer and said polyepoxide, and molding and reacting said polymer saidcrosslinking agent and said graded rubber particles, said graded-rubberparticles consisting essentially of (1) about 10 to about weight percenta core of crosslinked acrylic polymer consisting essentially of (a) amajor amount of a monofunctional monoacrylate constituting at a minimum80 mole percent, and (b) a minor and crosslinking amount of a diortrifunctional monomer containing two or more non-conjugated terminalethylenic groups, not exceeding about 20 mole percent of the corereactants, and (2) about 90 to about 10 weight percent an outer shellformed by polymerization of a mixture of monomers consisting essentiallyof about 30 to about 98 mole percent methyl methacrylate, 0 to about 68mole percent of unsaturated monomers selected from monofunctionalmonoacrylates, diacrylates, monovinyl hydrocarbons, and divinylhydrocarbons, and about 2 to about 35 mole percent of a monomer havingan olefinic group reactable with said methyl methacrylate and anepoxy-functional group which (a) remains unreacted in saidpolymerization and (b) provides said shell with surface functionalitythat is reactive with said polymer, of polymerized unsaturatedcompounds.

7. A method in accordance with Claim 6 wherein said core is formed fromabout 80 to about 98 mole percent of an ester of acrylic acid and a C -Cmonohydric alco hol and about 2 to about 20 mole percent of divinylbenzene, a diester of acrylic or methacrylic acid and a C C dihydricalcohol or a triester of acrylic or methacrylic acid and a C -Ctrihydric alcohol.

8. A method in accordance with Claim 6 wherein said functionality ofsaid polymer of polymerized unsaturated compounds is carboxyfunctionality.

9. A method in accordance with Claim 6 wherein said functionality ofsaid polymer of polymerized unsaturated compounds is epoxyfunctionality.

10. A method in accordance with Claim 6 wherein said functionality ofsaid polymer of polymerized unsaturated compounds is hydroxyfunctionality.

11. In a molded, thermoset, polymeric material comprising a polymer anda crosslinking agent reacted there with, the improvement wherein A. saidcrosslinking agent is a graded-rubber particle consisting essentially of(1) about to about 90 weight percent of a core of crosslinked acrylicpolymer consisting essentially of (a) a major amount of a monofunctionalmonacrylate constituting at a minimum about 80 mole percent, and (b) aminor and crosslinking amount of a dior tri functional monomercontaining two or more non-conjugated terminal ethylenic groups notexceeding about 20 mole percent of the core reactants, and (2) about 90to about 10 weight percent an outer shell formed by polymerization of amixture of monomers consisting essentially of about 30 to about 98 molepercent methyl methacrylate, 0 to about 68 mole percent of unsaturatedmonomers selected from monofunctional monoacrylates, diacr'ylates,monovinyl hydrocarbons, and divinyl hydrocarbons, and about 2 to about35 mole percent of a monomer having an olefinic group reactable withsaid methyl methacrylate and an epoxy-functional group which (a) remainsunreacted in said polymerization and (b) provides said shell withsurface functionality that is reactive with said polymer, of polymerizedunsaturated compounds and B. said polymer of polymerized unsaturatedcompounds has functionality selected from carboxy functionality, epoxyfunctionality and hydroxy functionality and being present in acrosslinking amount.

12. A molded, thermoset, polymeric material in accordance with Claim 11wherein said core is formed from about 80 to about 98 mole percent of anester of acrylic acid and a C -C monohydric alcohol and about 2 to about20 mole percent of divinyl benzene, a diester of acrylic or methacrylicacid and a C -C dihydric alcohol or a triester of acrylic or methacrylicacid and a C -C trihydric alcohol.

13. A molded, thermoset, polymeric material in accordance with Claim 11wherein said functionality of said polymer of polymerized unsaturatedcompounds is carboxy functionality.

14. A molded, thermoset, polymeric material in accordance with Claim 11wherein said functionality of said polymer of polymerized unsaturatedcompounds is epoxy functionality.

15. A molded, thermoset, polymeric material in accordance with Claim 11wherein said functionality of said polymer of polymerized unsaturatedcompounds is hydroxy functionality.

16. In a molded, thermoset, polymeric material wherein a polymer ofpolymerized unsaturated compounds having functionality selected fromcarboxy functionality, epoxy functionality and hydroxy functionality anda poly epoxide having at least two epoxy groups per molecule reactedtherewith in crosslinking amounts, the improvement which comprises thedispersion throughout said ther- 16' moset polymeric material ofgraded-rubber particles which are reacted with said polymer, said orboth said polymer and said polyepoxide, said graded-rubber particlesconsisting essentially of:

(1) about 10 to about 90 weight percent a core of crosslinked acrylicpolymer consisting essentially of (a) a major amount of a monofunctionalmonoacrylate constituting at a minimum mole per cent, and (b) a minorand crosslinking amount of a dior trifunctional monomer containing twoor more non-conjugated terminal. ethylenic groups not exceeding about 20mole percent of the core reactants, and (2) about to about 10 weightpercent an outer shell formed by polymerization of a mixture of monomersconsisting essentially of about 30 to about 98 mole percent methylmethacrylate, 0 to about 68 mole percent of unsaturated monomersselected from monofunctional monoacrylates, diacrylates, monovinylhydrocarbons, and divinyl hydrocarbons, and about 2 to about 35 molepercent of a monomer hav ing an olefinic group reactable with saidmethyl methacrylate and an epoxy-functional group which (a) remainsunreacted in said polymerization and (b) provides said shell withsurface functionality that is reactive with said polymer, of polymerizedunsaturated compounds.

17. A molded, thermoset, polymeric material in accordance with Claim 16wherein said core is formed from about 80 to about 98 mole percent of anester of acrylic acid and a C -C monohydric alcohol and about 2 to about20 mole percent of divinyl benzene, a diester of acrylic or methacrylicacid and a C -C dihydric alcohol or a triester of acrylic or methacrylicacid and a C -C trihydric alcohol.

18. A molded, thermoset, polymeric material in accordance with Claim 16wherein said functionality of said polymer of polymerized unsaturatedcompounds is carboxy functionality.

19. A molded, thermoset, polymeric material in accordance with Claim 16wherein said functionality of said polymer of polymerized unsaturatedcompounds is epoxy functionality.

20. A molded, thermoset, polymeric material in accordance with Claim 16wherein said functionality of said polymer of polymerized unsaturatedcompounds is hydroxy functionality.

References Cited UNITED STATES PATENTS 3,502,745 3/ 1970 Minton 260-8813,423,481 1/1969 Mizutani 260--836 3,437,514 4/ 1969 Burlant 117-93313,450,796 6/ 1969 Griflin 260-885 3,528,844 9/ 1970 Burlant 260-885 PAULLIEBERMAN, Primary Examiner U.S. Cl. X.R.

